1. Field of the Invention
The present invention relates to an apparatus and method for bar code reading, wherein the surface of an object on which a bar code is carried is scanned in raster fashion and the bar code is read using the reflected light.
2. Description of the Related Art
A bar code symbol, defined by the Universal Product Code (UPC), contains guard bars placed at both edges of the bar code and center bars placed at the center. A bar code encoding a 6- or 4-digit number (6 or 4 characters) is placed between the left guard bars and the center bars (the left block), and a bar code encoding the same number of characters is placed between the right guard bars and the center bars (the right block).
The surface of an object carrying a bar code is scanned in raster fashion to read the bar code. In scanning, if the bar code is placed with its vertical bars oriented substantially perpendicular to the direction of scanning, the left and right blocks can be scanned with one scan line and all the characters represented in both blocks can be demodulated from the data obtained from the one scan line. However, in an actual operating environment, it is not possible to demand that the direction of scanning be always perpendicular to the bars. In actual systems, to enable demodulation even when the bar code is placed over the scanning system at such an angle that the left and right blocks cannot be scanned simultaneously with one scan line but can be scanned with separate scan lines in different paths, provisions are made so that the left and right blocks are demodulated separately and the demodulation is complete after demodulating both blocks. In such systems, however, if the inclination of the bars is large, after first detecting one block a number of scans is required before the other block can be detected. In such cases, a large volume of unprocessable data is stored in a buffer, since the speed of demodulation is generally slower than the speed of scanning. Therefore, when the inclination of the bars is large, the time from the beginning of detection to the completion of demodulation becomes long because of the time taken to process a large volume of unprocessable data, the resulting problem being a slow system response. If the buffer capacity is reduced to reduce the amount of storable unprocessable data, this will in turn lead to a failure to capture necessary data, which also causes a slow response.